Documentation Source Text

    2|0|0|SCAN TABLE t2 (~1000000 rows)
    2|0|0|USE TEMP B-TREE FOR ORDER BY
    0|0|0|COMPOUND SUBQUERIES 1 AND 2 (EXCEPT)
</codeblock>)^

<h1>Sample Code</h1>

<p>Sometimes, within a large application, it may be inconvenient to modify
code to generate EXPLAIN QUERY PLAN commands for the SELECT queries being
investigated. From within an interactive debugging session, it may be almost
impossible. In these situations, a function similar to the following may
be useful. This particular function is passed an SQLite statement handle as an
argument and outputs the corresponding EXPLAIN QUERY PLAN report to standard
output. Application specific versions may output the report to an application
log or similar.

<!--
** WARNING: The following function, printExplainQueryPlan() is duplicated
** in file test1.c of the source distribution for testing purposes. If
** the code below needs to be modified, the copy in test1.c should also
** be modified and the Tcl tests run.
-->
<codeblock>
/*
** Argument pStmt is a prepared SQL statement. This function compiles
** an EXPLAIN QUERY PLAN command to report on the prepared statement,
** and prints the report to stdout using printf().
*/
int printExplainQueryPlan(sqlite3_stmt *pStmt){
  const char *zSql;               /* Input SQL */
  char *zExplain;                 /* SQL with EXPLAIN QUERY PLAN prepended */
  sqlite3_stmt *pExplain;         /* Compiled EXPLAIN QUERY PLAN command */
  int rc;                         /* Return code from sqlite3_prepare_v2() */

  zSql = sqlite3_sql(pStmt);
  if( zSql==0 ) return SQLITE_ERROR;

  zExplain = sqlite3_mprintf("EXPLAIN QUERY PLAN %s", zSql);
  if( zExplain==0 ) return SQLITE_NOMEM;

  rc = sqlite3_prepare_v2(sqlite3_db_handle(pStmt), zExplain, -1, &pExplain, 0);
  sqlite3_free(zExplain);
  if( rc!=SQLITE_OK ) return rc;

  while( SQLITE_ROW==sqlite3_step(pExplain) ){
    int iSelectid = sqlite3_column_int(pExplain, 0);
    int iOrder = sqlite3_column_int(pExplain, 1);
    int iFrom = sqlite3_column_int(pExplain, 2);
    const char *zDetail = (const char *)sqlite3_column_text(pExplain, 3);

    printf("%d %d %d %s\n", iSelectid, iOrder, iFrom, zDetail);
  }

  return sqlite3_finalize(pExplain);
}
</codeblock>